Cementitious spray applied fireproofing is not a new concept. For example, it is well known to spray apply fireproofing slurries to metal structural members and other building surfaces in order to provide a heat resistant coating thereon. U.S. Pat. Nos. 3,719,513 and 3,839,059, which are incorporated herein by reference, disclosed gypsum-based formulations that contain, in addition to the gypsum binder, a lightweight inorganic aggregate such as vermiculite, a fibrous substance such as cellulose, and an air entraining agent.
Geopolymer types of concrete include “alkali-activated fly ash geopolymer” and “slag-based geopolymer cement.” (There is often confusion between the meanings of the terms ‘geopolymer cement’ and ‘geopolymer concrete’. A cement is a binder, whereas concrete is the composite material resulting from the mixing and hardening of cement with water (or an alkaline solution in the case of geopolymer cement), and aggregates dispersed in the binder.)
Fly ash, also known as “pulverized fuel ash” in the United Kingdom, is a coal combustion product of fine particles that are driven out of the boiler with the flue gases. Ash that falls in the bottom of the boiler is called bottom ash. In modern coal-fired power plants, fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys. Depending upon the source and makeup of the coal being burned, the components of fly ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline), aluminum oxide (Al2O3) and calcium oxide (CaO), the main mineral compounds in coal-bearing rock strata. In the past, fly ash was generally released into the atmosphere, but air pollution control standards now require that it be captured prior to release by fitting pollution control equipment. In the US, fly ash is generally stored at coal power plants or placed in landfills. About 43% is recycled, often used as a pozzolan to produce hydraulic cement or hydraulic plaster and a replacement or partial replacement for Portland cement in concrete production. Pozzolans ensure the setting of concrete and plaster and provide concrete with more protection from wet conditions and chemical attack.
The burning of harder, older anthracite and bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 7% lime (CaO). Possessing pozzolanic properties, the glassy silica and alumina of Class F fly ash requires a cementing agent, such as Portland cement, quicklime, or hydrated lime—mixed with water to react and produce cementitious compounds. Alternatively, adding a chemical activator such as sodium silicate (water glass) to a Class F ash can form a geopolymer. Notably, geopolymer cements rely on such minimally processed natural materials or industrial byproducts to significantly reduce its carbon footprint, while also being very resistant to many common concrete durability issues.
Fly ash produced from the burning of younger lignite or sub-bituminous coal, in addition to having pozzolanic properties, also has some self-cementing properties. In the presence of water, Class C fly ash hardens and gets stronger over time. Class C fly ash generally contains more than 20% lime (CaO), and unlike Class F, self-cementing Class C fly ash does not require an activator. Alkali and sulfate (SO4) contents are generally higher in Class C fly ashes.
The slag-based geopolymer cement often uses a granulated, ground, blast furnace slag (GGBFS) which is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.
Recycling fly ash and GGBFS materials have become increasing popular in recent years due to increasing landfill costs, interest in sustainable development, and reduced carbon footprint for buildings.
The use of geopolymer types of cement and concrete formulations in spray-applied fireproofing is relatively new. Geopolymer types of cement have a heat resistance that is typically relatively high when compared to Portland cement, but there are challenges in using this material as a fireproof coating.
WO 2015/144796A1 discloses a fireproofing cementitious coating composition containing organic polymers and blast furnace slag. The invention provides a composition having a bulk density of 0.8 g/cm3 or less comprising (a) 25-65 weight % of an inorganic binder comprising (i) 83 to 100 weight % of calcium aluminate cement, (ii) 0 to 14 weight % of calcium sulphate, (iii) 0 to 9 weight % of Portland cement wherein the weight % of (i), (ii), (iii) is based on the sum of (i)+(ii)+(iii), (b) 0.5-15 weight % of one or more organic polymers, (c) 30-75 weight % of one or more inorganic fillers wherein the bulk density of the fillers is less than 0.5 g/cm3, wherein weight % is calculated on the total weight of all the non-volatile components in the composition.
U.S. Pat. No. 5,718,759 discloses a fire-stopping cementitious material made from pozzolanic aggregate and a blend of Portland cement and ground blast slag (Column 1, Lines 15-20; Column 1, Lines 58-67; Column 2, Lines 57-65; Column 6, Lines 5-24). A cementitious composition is disclosed which is useful for water-resistant construction materials, including floor underlayments, backing boards, self-leveling floor materials, road patching materials, fiberboard, fire-proofing sprays, and fire-stopping materials includes about 20 wt. % to about 75 wt. % calcium sulfate beta-hemihydrate, about 10 wt. % to about 50 wt. % Portland cement, about 4 wt. % to about 20 wt. % silica fume and about 1 wt. % to about 50 wt. % pozzolanic aggregate. The Portland cement component may also be a blend of Portland cement with fly ash and/or ground blast slag.
U.S. Pat. No. 8,519,016 discloses a lightweight cementitious binder composition containing fly ash, alkali metal salt of citric acid, alkali metal silicate, foaming agent for entraining air, and water (Column 3, Lines 46-62; Column 4, Lines 20-25; Column 4, Lines 60-67; Column 8, Lines 1-5). The invention is directed toward a method of making a lightweight cementitious binder composition with improved compressive strength for products such as cementitious panels. The method mixes fly ash, alkali metal salt of citric acid, alkali metal silicate, foaming agent for entraining air, water and in the preferred embodiment a foam stabilizing agent. Compositions which include fly ash selected from the group consisting of class C fly ash, class F fly ash and mixtures thereof, alkali metal salts of citric acid, alkali metal silicates, foaming agents, and preferably a foam stabilizer, such as polyvinyl alcohol, and do not require use of set retarders. Compositions containing class F fly ash can optionally contain Type III Portland cement.
U.S. Pat. No. 8,167,998 discloses a lightweight ready-mix concrete composition containing coarse aggregate combination such as ground granulated blast furnace slag, fly ash, glass, silica, expanded shale, perlite, and/or vermiculite, as well as set retarders such as borates. In its broadest context, the patent discloses a lightweight ready-mix concrete composition that contains 8-20 volume percent cement, 11-50 volume percent sand, 10-31 volume percent prepuff particles, 9-40 volume percent coarse aggregate, and 10-22 volume percent water, where the sum of components used does not exceed 100 volume percent. The prepuff particles have an average particle diameter of from 0.2 mm to 8 mm, a bulk density of from 0.02 g/cc to 0.64 g/cc, an aspect ratio of from 1 to 3. The slump value of the composition measured according to ASTM C 143 is from 2 to 8 inches. After the lightweight ready-mix concrete composition is set for 28 days, it has a compressive strength of at least 1400 psi as tested according to ASTM C39.
WO 2016/016385A1 discloses a geopolymer used as a binder for fire resistant insulating material (Page 1, Lines 3-7; Page 6, Lines 2-9; Page 7, Lines 30-33; Page 8, Lines 5-15). The reference illustrates use of a geopolymer in a coating composition for a building construction component, a coated component for use in building construction wherein the coating comprises a geopolymer, a method of coating a component comprising applying a curable geopolymer mixture to a surface of the component and curing the mixture to form a cured geopolymer coating, and the use of a geopolymer as a mortar.
U.S. Patent Publication No. 2014/0047999 discloses an acid and high temperature resistant cement composite containing fly ash and ground slag. The patent is largely directed toward a process for the production of acid and high temperature resistant cement composites, where the matrix is alkali activated F fly ash alone, F Fly ash combined with ground slag or ground slag alone. F-fly ash produces lower quality alkali activated cement systems. On the other hand, the lack of calcium oxide results in very high resistance to medium and highly concentrated inorganic or organic acids. The high strength and low permeability of pure F-fly ash cement systems is achieved by using in the composition un-densified silica fume, the amorphous silicon dioxide obtained as by products in production of ferro-silicones. Precipitated nano-particle silica made from soluble silicates and nano-particle silica fume produced by burning silicon tetra chloride in the hydrogen stream.
U.S. Patent Publication No. 2015/0321954 discloses a geopolymer cement containing fly ash and granulated blast furnace slag. The patent discloses a solid component activator for use in a geopolymer cement containing a silico-aluminate material comprising a mixture of sodium silicate and sodium carbonate for activating the geopolymer cement by increasing reactivity of the silico-aluminate material in the geopolymer cement when forming geopolymer concrete.
EP 0807614B1 discloses a spraying concrete containing calcium aluminate glass, aluminum silicate, and pozzolanic material.
Additional problems exist with previous fireproofing treatments. For example, architects have many specifications for building structures and the components that make up their hidden and exposed infrastructures. Such specifications can also include the equilibrium density of any applied fireproof coating. Typical specifications are 15, 20, 25, 40 and 50 pounds per cubic foot.
An applied fireproof coating is preferably done by spraying with conventional spraying equipment although coating repairs may be done with a higher viscosity material and a trowel. The applied coating should also exhibit good rheological strength, cure fully and without substantial shrinkage, and exhibit good bond strength to the applied substrate.
Two types of standard tests are used to measure fire resistance of applied coatings on a metal substrate. Both measure the time required for the protected substrate to reach 1000° F. This time is generally understood the time provided to allow occupants of the protected structure to escape. Thus, a longer time means a longer period for evacuating the structure.
The first test is found in ANSI/UL263 “Fire Tests of Building Construction Materials.” (The ANSI/UL263 test is equivalent to ASTME119.) This test applies an increasing level of heat up to 2000° F. over a designated period of time. The second test is ANSI/UL1709 “Rapid Rise Fire Tests of Protection Materials for Structural Steel” that applies the 2000° F. heat over 5 minutes. The ANSI/UL1709 test is generally considered to be the more severe test.
It would be desirable to have an effective geopolymer coating that could be applied by spraying, troweling or similar techniques that can apply an effective fire-resistive coating to a building infrastructure.
It would also be desirable to have fire resistant geopolymer coating that exhibited good rheological strength, bond strength, and good durability.
It would also be desirable to have a geopolymer coating that could be adjusted to a specified equilibrium density upon curing to meet various building specifications and that would exhibit good fire-resistance times with the applicable testing standards.